Joule Thomson

Referring to the change in temperature observed when a gas expands while flowing through a restriction without any heat entering or leaving the system. The change may be positive or negative. For each gas, there is an inversion point that depends on temperature and pressure, below which it is cooled and above which it is heated. For example, for methane at 100oC [212oF], the inversion point occurs at about 500 atmospheres [7350 psi]. The magnitude of the change of temperature with pressure depends on the Joule-Thomson coefficient for a particular gas.
The Joule-Thomson effect often causes a temperature decrease as gas flows through pores of a reservoir to the wellbore.